A display device having a plurality of pixels formed over a substrate has been known. As a typical example of such a display device, a liquid crystal display device and an EL display device are represented.
An EL display device is a display device having a light-emitting element with a structure in which a material exhibiting an electroluminescence (EL) phenomenon is sandwiched between a pair of electrodes in each pixel. A light-emitting element using an organic compound as a material is called an organic light-emitting element, an organic EL element, or an organic electroluminescence element. A display device having a plurality of such organic light-emitting elements is called an organic EL display device. Apart from a liquid crystal display device, an organic EL display device is characterized in being a thin display device since a backlight is not necessary. Furthermore, an EL display device is expected to be applied as the so-called flexible display device because an EL display device is an all-solid display device.
Generally, each pixel includes a light-emitting element and a transistor for driving the light-emitting element, and a variety of wirings is laid out over a substrate in order to control the transistor or supply a current to the light-emitting element. For example, a variety of layouts regarding the wirings and pixels is disclosed in Japanese patent application publications No. 2006-86333, 2012-238005, 2014-191650, and 2015-84104.